The present invention pertains generally to the field of computer card modules and the frames contained within the modules. More specifically, the present invention relates generally to circuit card modules having frames that improve the cooling properties of the modules but optionally remain compliant with Institute of Electrical and Electronics Engineers (IEEE) specifications.
Commercially-available, off-the-shelf components that are included in circuit card modules are often unreliable when exposed to the high temperatures present in, for example, the military environment. This is due to the ineffectiveness of conventional methods of controlling component junction temperatures under stringent temperature conditions. Conventional cooling methods utilized in off-the-shelf parts include normal convection, forced convection--such as fan cooling, liquid cooling, various forms of heat conductors or sinks, etc.--and combinations of two or more of these methods. Numerous patents have issued to structural designs having cooling properties for use with circuit card modules. For example, U.S. Pat. No. 5,280,411, issued to Dirks et al. discloses the addition of heat conducting rails to the edges of a circuit card. Meyer, IV et al., in U.S. Pat. No. 5,549,155, teaches the use of a heat conductive p and a heat pipe to disperse the unwanted heat from a computer chip. U.S. Pat. Nos. 5,532,430 and 5,559,675, of Lanoe and Hsieh et al., respectively, disclose heat dissipating structures for use with circuit cards. In U.S. Pat. No. 4,916,575, Van Asten discusses the use of a ribbed frame, which is structured to hold multiple cards. Several patents, including U.S. Pat. Nos. 4,558,395; 5,482,109; 5,714,789; and 5,625,227, disclose the use of a circulating coolant system to remove the generated heat. However, none of these patents disclose or suggest a structure that satisfies the IEEE 1101.2 standards (i.e., IEEE Standard for Mechanical Core Specifications for Conduction-Cooled Eurocards), which specifies convection-cooled chassis requirements and conduction-cooled chassis requirements.
The prior art has also recognized the utility of additional force at the contact points between module structures and the computer chassis. Morrison, U.S. Pat. No. 4,994,937, and Moser, U.S. Pat. No. 5,262,587, teach clamping structures to achieve this goal. Buzzelli, in U.S. Pat. No. 4,853,829, discloses a locking mechanism having a sliding block which holds the module to the heatsink plate. As mentioned above, none of these references appear to satisfy the IEEE standards of current interest.
The current methods for cooling commercial off-the-shelf circuit cards, such as Versa Module Eurocards (VMEs), are conduction-cooled modules that operate in a conduction-cooled chassis or a convection-cooled chassis, such as described in IEEE 1101.2 Specifications. In order to comply with the IEEE 1101.2 Specifications, the cards must be mechanically compliant with both chassis types. This requires an approximately 0.063" thick.times.0.098" wide protrusion along the card edge to engage the convection-cooled chassis card guides. This protrusion is often an extension of the printed wiring board (PWB) or machined as part of PWB. A challenge posed by the IEEE 1101.2 Specifications is that the card modules must be compatible with existing forced-air cooled chassis or racks, which do not use wedgelocks for heat exchange or mechanical mounting. Instead, the existing forced-air cooled chassis use the edge of the PWB as a guide and one of the mechanical attachment points for the chassis. In the convection-cooled configuration, air flow over the card is used to remove component heat. In the conduction-cooled configuration, the component heat is removed by conduction to the chassis cold wall. The heat is then removed from the chassis by external means. The protrusion reduces the efficiency of heat removal by reducing the available conduction contact area and by reducing the size of the wedgelock that can be used. These two effects reduce the efficiency of movement of the heat to the cold wall of the chassis. Because of these legacy requirements, the conduction-cooled modules do not take full advantage of the area available at the cold wall of the chassis.
Accordingly, it is an object of the present invention to provide a circuit card module with improved cooling efficiency that has a stiffening frame for the circuit cards and a mounting structure to allow it to be optionally compliant with the IEEE 1101.2 chassis structure.
It is a further object of the present invention to improve the cooling efficiency of the circuit card module by developing a frame structure which provides a more direct path for the dissipation of heat from the components of the circuit card.
It is another object of the present invention to increase the conduction contact area between the circuit card module and the chassis.
It is still a further object of the present invention to improve the cooling efficiency of the module through the use of a larger wedgelock.
It is yet a further object of the present invention to make the frame/wedgelock assembly interchangeable with a conventional frame so that the module can be used with either conduction-cooled chassis or convection-cooled chassis.